The invention pertains to a fuel injection nozzle for internal combustion engines, having a needle valve which opens toward the inside and which is constrained by a closure spring disposed within a spring chamber positioned thereabove and further includes an axially displaceable and closely fitting intermediate piston which includes a portion that extends into the spring chamber at the side remote from the needle valve and cooperates with the needle valve at least some of the time.
In a known fuel injection nozzle, the intermediate piston acts upon the needle valve during the entire fuel injection operation, and thereby influences the entire fuel injection process. The intermediate piston in such devices is influenced, on the side remote from the needle valve, by a fuel pressure which varies in accordance with the pressure of the fuel delivered to the nozzle for the fuel injection operation. Accordingly, with such devices it is known that the pressure upon this intermediate piston also decreases toward the end of the fuel injection supply operation as the delivery pressure decreases, and further that by decreasing the force of the intermediate piston which acts in the direction of closure of the needle valve will result in a protraction of the fuel injection termination and, accordingly, corresponding deterioration of the exhaust gas valve.